Photosensitive materials with ever-improving properties are of great importance for optical and photonics applications. Additionally, they are extremely useful for designing components for neutron optical devices. We provide an overview on materials that have been tested and successfully used to control beams of cold and very cold neutrons based on diffractive elements. Artificial gratings are generated and optimized for the specific application in mind. We discuss the needs of the neutron optics community and highlight the progress obtained during the last decade. Materials that have been employed so far along with their properties are summarized, outlining the most promising candidates for the construction of an interferometer for very cold neutrons.
A photopolymerizable nanoparticle-polymer composite (NPC) is a novel nanocomposite photopolymer that is dispersed with inorganic nanoparticles having a large refractive-index difference from that of the formed polymer. In order to realize the uniform and high dispersion of nanoparticles without any aggregation, we employ nanostructured polymers that possess highly branched main chains, the so-called hyperbranched polymer (HBP), as size and refractive-index controllable organic nanoparticles with its ultrahigh refractive index. We show that high dispersion of the ultrahigh refractive index HBP in a photopolymerizable NPC provides a volume holographic grating possessing the saturated refractive modulation amplitude as large as 0.03 at grating spacing of 0.5-μm in all the visible spectral regions of the red (640nm), the green (532nm) and the blue (405nm). Such a high contrast volume holographic grating can be used for volume optical holographic elements in a wearable headset for augmented and mixed reality.
We report our latest results on holographic gratings based on nanoparticle-polymer composites (NPC) including nanodiamonds with large refractive index modulation amplitude for cold and very cold neutrons (1 nm < λ < 10 nm). Diamond has the best combined neutron optical properties: high coherent scattering length, low incoherent scattering and low absorption. These unique properties allowed us to create phase gratings with large refractive index modulation, high thermal and mechanical stability, and also exhibiting large area holograms compared to NPC gratings incorporating other types of nanoparticles. We discuss the measured light and neutron diffraction properties of nanodiamond NPC gratings. It is shown that the NPC gratings exhibit extremely large scattering length density modulation amplitudes and as a result high diffraction efficiencies for cold and very-cold neutrons. We also discuss possible applications of nanodiamond NPC gratings in neutron optics.
In the second part of our presentations we discuss the results of diffraction experiments from nanodiamond-polymer composite gratings performed with slow neutrons, i.e., at wavelengths longer than a nanometer. One goal of our investigations is to develop flexible, handy, low cost neutron diffractive optical elements (gratings) which can be tailored to serve as mirrors, two-port beamsplitters, multiport beamsplitters, polarizing beamsplitters or even can be assembled to form an interferometer. Basically three adjustable multiplicative parameters are decisive for the performance, i.e., the reflectivity or diffraction efficiency, of such gratings: the wavelength of the neutrons, the thickness and the neutron scattering density modulation of the grating. While the _rst is solely determined by the application one has in mind, the second parameter can be adjusted during the production process of the sample or by tilting the grating about an axis parallel to the grating vector, thus increasing the effective thickness. The third parameter, however, can only be tuned via the production process of the gratings but offers an enormous flexibility due to a variety of nanoparticles and the polymeric host materials at hand. For neutrons the important criteria are to design gratings having high coherent scattering length density modulation while avoiding incoherent scattering and absorption at the same time. For interferometric purposes an ideal grating will have high reflectivity and low angular selectivity. Here, we show first results obtained with nanodiamond-polymer composite gratings and outline potential ways to improvements.
We demonstrate for the first time the use of nanodiamond in constructing holographic nanoparticle-polymer composite transmission gratings with large saturated refractive index modulation amplitudes at both optical and slow-neutron wavelengths, resulting in efficient control of light and slow-neutron beams. This is so because nanodiamond possesses a high refractive index at optical wavelengths and large coherent and small incoherent scattering cross sections with low absorption at slow-neutron wavelengths. In the first part of the work we describe the synthesis of nanodiamond, the preparation of photopolymerizable nanodiamond-polymer composite films, the construction of transmission gratings in nanodiamond-polymer composite films and light optical diffraction experiments. Experiments of slow-neutron diffraction from such gratings will be described in the second part.
We report on an experimental investigation of recording a plane-wave volume holographic transmission grating in a photopolymerizable nanoparticle-polymer composite film dispersed with hyperbranched-polymer (HBP) organic nanoparticles in an acrylate monomer blend codoped with an electron donor and acceptor photoinitiator/inhibitor system. The HBP organic nanoparticle possesses the ultrahigh refractive index of 1.82 at 532 nm owing to the inclusion of triazine and aromatic ring units, which provides a large difference in the refractive index between HBP and the formed polymer. It is found that the recorded NPC grating with 23 vol.% HBP dispersion possesses the saturated refractive index modulation amplitude as large as 4.5 x 10-2 at 532 nm and at recording intensities of a few mW/cm2. Obtained results suggest the use of our newly developed HBP-dispersed NPC as volume optical holographic elements for wearable display for augmented and mixed reality.
It is well known that in standard diffaction experiments only the amplitudes of structural Fourier components are recovered but phase information is lost. This problem is known as the ’phase problem’ in crystallography. In this contribution, we point out how the phase problem of diffraction can be solved in some particular cases by employing multi-wave interference. In the experimental situation described here, we were able to determine the form of the refractive-index profile of a 1-D nanocomposite holographic grating by using a multi-wave coupling analysis of the measured angular dependence of the diffraction efficiencies for a number of diffraction orders.
We investigate the spatial frequency response of a volume grating recorded in a ZrO2 nanoparticle-dispersed nanocomposite. We experimentally find that there exists the optimum recording intensity to maximize the saturated refractive index modulation amplitude of a nanocomposite grating recorded at short and long grating spacing. A strong parametric relationship between grating spacing and recording intensity is seen and an increase in the saturated refractive index modulation amplitude at shorter grating spacing (< 0.5 μm)can be obtained by using higher recording intensities than those at longer grating spacing. Such a trend can be qualitatively explained by a phenomenological model used for holographic polymer-dispersed liquid crystal gratings. We also describe another method for the improvement of the high spatial frequency response by co-doping of thiol monomer that acts as a chain-transfer agent.
The photopolymerizable nanoparticle-polymer composites (NPCs) have thus far shown their excellent performance in practical applications, such as holographic data storage, nonlinear optics and neutron optics. We have demonstrated twofold enhancement of the saturated refractive index modulation (Δnsat) of ZrO2 NPC volume gratings recorded at high spatial frequencies by doping with a single functional thiol as a chain transfer agent (CTA). This result suggested that the incorporation of a CTA in an NPC is very useful for holographic applications of volume gratings in light and neutron optics. Such chemical modification of NPC volume gratings may be more effective by doping with multifunctional thiols. This is so because polymer features such as the molecular weight and the crosslinking network density can be tailored more diversely by introducing multifunctional thiols in photopolymers. The influences of varying functionalities of thiols as chain transfer agents on the thermal stability of a volume grating recorded in a photopolymerizable ZrO2 nanoparticle-polymer composite film have been investigated.
We report on the characterization of volume holographic gratings recorded in photopolymerizable nanocomposites incorporated with hyperbranched polymer (HBP) acting as transporting organic nanoparticles. The HBP possesses ultrahigh index of refraction owing to the inclusion of triazine and aromatic ring units. Such an HBP was easy to disperse into acrylate monomer without any aggregation, so that films with good optical quality are available. A transmission volume grating with refractive index changes up to 2.3×10-2 was obtained at 27 vol.% HBP concentration and 7 vol.% multifunctional acrylate monomer at a wavelength of 532 nm.
We review our experimental investigations of photopolymerizable nanoparticle-polymer composites (NPCs) for holography and diffractive optics. Various types of hyperbranched polymer (HBP) were systhesized and used as transporting organic nanoparticles. These HBPs include hyperbranched poly(ethyl methacrylate) (HPEMA), hyperbranched polystyrene (HPS) and hyperbranched triazine/aromatic polymer units (HTA) whose refractive indices are 1.51, 1.61 and 1.82, respectively. Each HBP was dispersed in (meth)acrylate monomer whose refractive index was so chosen that a refractive index difference between HBP and the formed polymer was large. Such monomer-HBP syrup was mixed with a titanocene photoinitiator for volume holographic recording in the green. We used a two-beam interference setup to write an unslanted transmission volume grating at grating spacing of 1 μm and at a wavelength of 532 nm. It is shown that NPC volume gratings with the saturated refractive index modulation amplitudes as large as 0.008, 0.004 and 0.02 can be recorded in NPCs incorporated with HPEMA, HPS and HTA at their optimum concentrations of 34, 34 and 25 vol.%, respectively. We show the usefulness of HBP-dispersed NPC volume gratings for holographic applications such as holographic data storage and diffractive optical devices.
We describe an experimental investigation of volume holographic recording in photopolymerizable thiol-ene based nanoparticle-polymer composites (NPCs) at a wavelength of 404 nm. We introduce a new photoinitiator, Irgacure819, for efficient volume holographic recording in the blue-violet spectral region and measure the photopolymerization dynamics and the holographic recording properties at its varying concentrations. It is found that doping of 0.1 wt.% Irgacure 819 provides the saturated refractive index modulation amplitude as large as 9.5×10−3 and the material recording sensitiviey as high as 1800 cm/J. These measured values are much larger than the minimum required values for holographic data storage media. It is also shown that the out-of-plane shrinkage can be suppressed more with decreasing the photoinitiator concentration. We compare these results with another blue sensitizer, Darocur TPO, to evaluate the performance of Irgacure 819.
We report on the volume holographic grating formation in photopolymerizable polymer nanocomposites that incorporate new hyperbranched polymers (HBPs) acting as transporting organic nanoparticles. Since HBPs are easily dispersed to acrylate monomer without any aggregation and possesses ultrahigh index of refraction of the order of 1.8 in the green due to the inclusion of triazine and aromatic ring units, volume gratings with good optical quality and refractive index changes as large as 2.2 × 10−2 can be recorded. It is also shown that the out-of-plane thickness change due to polymerization shrinkage is reduced to 2% or lower by the HBP dispersion.
Photopolymerizable nanoparticle-polymer composites (NPCs) have thus far shown their excellent performance in various applications, such as holographic data storage, nonlinear optics and neutron optics. Specifically, for such applications, a high spatial frequency material response is necessary, as it is the response to high spatial frequencies that determines their spatial resolution and diffraction properties. However, it is known that the spatial frequency response of a recorded hologram in multi-component photopolymers including NPCs and holographic polymer-dispersed liquid crystals exhibits a reduction in refractive index modulation at high spatial frequencies. In order to overcome this drawback, an addition of chain transfer agents (CTAs) may be useful as done for all-organic photopolymers to modify their nonlocal response and phase separation characteristics. In our work, we investigate the effect of CTAs on the spatial frequency response in NPCs. Here we employ various chain-transfer agents with three different thiol groups in a photopolymerizable ZrO2 NPC film. A range of CTA concentration is carried out, in order to explore the most effective material combination used in the examination of spatial frequency response. The significant improvement in spatial frequency response of NPCs through the addition of a CTA with the most appropriate concentration is presented.
We report on volume holographic recording in thiol-ene based nanoparticle-polymer composites (NPCs) at a wavelength of 404 nm by using a highly coherent blue diode laser. We study the photopolymerization dynamics of two types of thiol-ene based NPCs doped with different blue-sensitive initiator/sensitizer systems (Darocur ® TPO and Irgacure ® 784/BzO2) at various doping concentrations. We also characterize a volume holographic grating recorded in these two types of thiol-ene based NPCs. Such material characterization includes the refractive index modulation, the material recording sensitivity and polymerization shrinkage. It is shown that Darocur R _ TPO provides larger refractive index modulation and higher material recording sensitivity than those with Irgacure ® 784/BzO2 but these two blue-sensitive initiator/sensitizer systems amount to meeting the requirements of the refractive index modulation and the material recording sensitivity for holographic data storage. However, it is found that shrinkage reduction of a volume grating recorded in these two types of thiol-ene based NPCs at 404 nm is not as effective as the same thiol-ene based NPC doped with Irgacure ® 784/BzO2 at 532 nm.
We propose the use of radical-mediated thiol-yne step-growth photopolymerizations for volume holographic recording in NPC films to overcome the drawback of low crosslinking densities but retain the advantage of low shrinkage in the thiol-ene photopolymerizations. The thiol-yne photopolymerization mechanism is different from the thiol-ene photopolymeriztions in the sense that each alkyne functional group can react consecutively with two thiol functional groups. We show that thiol-yne based NPC films dispersed with silica nanoparticles give the saturated refractive index change as large as 0.008 and the material recording sensitivity as high as 2005 cm/J at a wavelength of 532 nm, larger than the minimum acceptable values of 0.005 and 500 cm/J, respectively, for holographic data storage. We also show that the shrinkage of a recorded hologram can be as low as that of thiol-ene based NPC films and that the thermal stability is improved better. In addition, we demonstrate digital data page recording in thiol-yne based NPC films, showing a low symbol error rate and a high signal-to-noise ratio to be 2.8×10−4 and 8, respectively.
We present a theoretical analysis of the closed-aperture Gaussian beam Z-scan for nonlinear optical materials
with both saturable absorption and simultaneous third- and fifth-order nonlinear refraction. We formulate a
theoretical expression for the Z-scan transmittance by means of the Adomian’s decomposition method and the
thin film approximation. It is applied to the experimental characterization of the nonlinear optical properties of a
semiconductor CdSe quantum dot-polymer nanocomposite film. We show that measured results of the open- and
closed-aperture Z-scan transmittances of the nanocomposite film are well explained by the theoretical model.
We report on a statistical thermodynamic simulation of holographic photopolymerization in a holographic
polymer-dispersed liquid crystal under holographic exposure. We employ the dynamic density functional theory
to study the spatio-temporal evolution of monomer, polymer and liquid crystal distributions as continuous density
order parameters in numerical simulations. Density-dependent mutual diffusion of monomer, polymer and
liquid crystals are taken into account under the constraints of the mass conservation and the incompressibility
conditions by using the Lagrange multiplier method. The autocatalytic model is employed to describe the photopolymerization
kinetics. The simulation results are compared with measured results such as the average size
of liquid crystal droplets and a grating-spacing dependence of the formed refractive index modulation.
We report on holographic storage of digital data pages in a thick silica nanoparticle-polymer composite film
that uses step-growth thiol-ene photopolymerization at a wavelength of 532 nm. Shift-multiplexed holographic
storage of 180 digital data pages with a two-dimensional 2:4 modulation code was successfully demonstrated
with low symbol-error rates. This result clearly shows the feasibility of the thiol-ene based nanoparticle-polymer
composite system as holographic data storage media.
Phenomenon of slow light has long been a hot research topic due to its promising and potential applications in
communication networks, signal processing, optical sensors and nonlinear interactions. Particularly, photonic crystal
devices, being capable of supporting slow-light propagation, are much attractive owing to its room-temperature operation
and tunable dispersion features. Among them, photonic crystal waveguides (PCWs) are specially used in compact
devices, while photonic band-gap fibers (PBGFs) are usually used in short-distance propagation and high sensitive
interferometers. In this paper, dispersion tailoring schemes for obtaining a high group index with the wide band and low
group velocity dispersion (GVD) are reviewed in both PCWs and PBGFs. For the same purpose, we propose schemes for
the slow-pulse propagation in PCWs based on the air-hole shifting method and in PBGFs based on the microfluid
infiltration method, respectively. Simulation results using 2D plane wave expansion method and finite-difference timedomain
(FDTD) method are given. Pulse distortion and design optimization are also discussed in some detail with the
consideration of the practical fabrication errors. Slow-light pulse propagation in photonic crystal fiber is also
demonstrated in the experiment based on stimulated Brillouin scattering.
We describe an experimental investigation of the photopolymerization kinetics and volume holographic recording
characteristics of silica nanoparticle-polymer nanocomposites using thiol-ene monomers capable of step-growth
polymerization. We characterize the visible light curing kinetics of a thiol-ene monomer system consisting of
secondary dithiol with high self-life stability and low odor and triene with rigid structure and high electron density
by using real-time Fourier transform spectroscopy and photocalorimetry. In plane-wave volume holographic
recording at a wavelength of 532 nm it is shown that while volume holograms recorded in the nanocomposites
exhibit high transparency, their saturated refractive index modulation (Δnsat) and material sensitivity (S) are as
large as 1x10-2 and 1615 cm/J, respectively. The polymerization shrinkage is reduced as low as 0.4% as a result
of the late gelation in conversion. These values meet the acceptable values for holographic data storage media
(i.e., 5x10-3, 500 cm/J and 0.5% for Δnsat, S and shrinkage, respectively). The improved thermal stability of
volume holograms recorded in the nanocomposites is also confirmed experimentally.
We describe an experimental investigation of the nonlinear optical properties of nanocomposites incorporating
organic (hyperbranched polymer)-metallic (Au or Pt) nanoparticle complex embedded in polymer films. Zscan
techniques are employed to measure the effective third-order nonlinear optical susceptibilities χ(3)
eff of the
composites with 35 ps pulses at 532 nm. The relative sign of the real and imaginary parts of χ(3)
eff could be
explained qualitatively by the Kramers-Kronig relation. The third-order nonlinear optical susceptibilities of Au
and Pt nanoparticles from the measured values for χ(3)
eff were also determined to be (-5.48 + 4.76i)×10-8 and
(4.43 - 0.65i)×10-6 esu, respectively, at 532 nm.
We demonstrate volume holographic recording in nanoparticle-polymer composites using thiol-ene monomers
capable of step-growth polymerization by which shrinkage can be reduced as low as 0.2%. The reduced shrinkage
is comparable to other low-shrinkage dry photopolymer systems such as those including a high content of inert
binder components and using monomers capable of cationic ring-opening polymerization. It is shown that the
thiol-ene based organic nanoparticle-polymer composites possess the refractive index modulation and the material
sensitivity of 8×10-3 and 1014 cm/J, respectively, in the green, larger than the minimum acceptable values of
0.005 and 500 cm/J for holographic data storage.
We report on the spectral transmittance and wavelength-dispersion properties of two-dimensional photonic lattices
using holographic polymer dispersed liquid crystals (HPDLCs) and demonstrate their electrical control.
A statistical thermodynamic model is employed to calculate spatial distributions of the formed polymer, liquid
crystal molecules and the resultant anisotropic refractive index distribution under three-beam holographic exposure.
The effect of multiple reflections inside an HPDLC film on the formed refractive index distribution is
also taken into account in the theoretical analysis. Measured transmittance spectra and wavelength-dispersion
angles are compared with the calculated results.
Slow-light technology via stimulated Brillouin scattering (SBS) in an optical fiber has attracted a lot of attention owing
to its flexible gain spectrum tailoring capacity, good compatibility with existing telecommunication systems, and great
application for photonic switchers and routers in ultra-high-speed photonic networks. In this paper we present a general
theoretical model for analyzing the dynamic behavior of the nonlinear interactions of the transient SBS process based on
the three-wave coupled-amplitude equations for the pump, Stokes and acoustic waves. Spatial and temporal evolution of
a generating slow-light pulse with the duration of sub-nanosecond under double broadband pump case is accurately
simulated owing to the fact that our model includes the second-order derivative of the acoustic field. We conclude that
the origin of the pulse broadening and distortion can be explained in terms of the temporal decay of the induced acoustic
field.
We report on the diffraction properties of a volume hologram recorded at a wavelength of 404 nm in a ZrO2
nanoparticle-polymer compsite film. It is found that the refractive index modulation and the material recording
sensitivity are as high as 8 × 10-3 and 9000 cm/J, respectively, at the ZrO2 nanoparticle concentration of 35
vol.% and a recording intensity of 5 mW/cm2. These values are comparable to or higher than those recorded at
a wavelength of 532 nm. Effects of the ZrO2 nanoparticle dispersion in acrylate monomer on the polymerization
kinetics are also examined by using a photo-differential scanning calorimeter. It is found that the incorporation
of ZrO2 nanoparticles increases the polymerization rate.
Slow-light techniques are promising for obtaining tunable delay lines which are potential candidates for bit
synchronization and buffer applications in optical packet switching networks. We describe a theoretical study on slowlight
in optical fibers based on stimulated Brillouin scattering (SBS). A general model for resonant three-wave nonlinear
interactions between a pump beam, an acoustic wave and a counterpropagating signal pulse is proposed. Analytic and
numerical solutions of the three-wave coupled equations are obtained for the steady-state and the transient regimes,
respectively. Space-time evolutions of a generating slow-light pulse for both small-signal and pump-depletion (or gainsaturation)
cases in the above two regimes are given and compared, for different pump powers and signal pulse widths.
The physical origin of broadening and distortion of slow-light pulse is discussed. Optimum design considerations for
undistorted slow-light signal propagation also are discussed.
We describe a theoretical analysis of broadband stimulated Brillouin scattering (SBS) slow light delay in a single-mode
optical fiber. A flat-top broadband SBS gain spectrum can be constructed by use of two broadband pump beams. We
propose two schemes of the double broadband pumping. We show that, for each scheme, the spectral profile of the total
SBS gain becomes wide and symmetric when the appropriate architecture of the two broadband pump beams is adopted accordingly. Our schemes can effectively reduce or even eliminate the broadening of signal pulse. It provides the use of shorter signal pulses for slow light control.
We report on measurements of thermal expansion coefficients and temperature-dependent refractive indices
of nanoparticle-polymer composite films in which plane-wave volume holograms are recorded. These physical
constants are evaluated for photopolymer films with the incorporation of inorganic nanoparticles or binder
polymer. We show that the incorporation of inorganic nanoparticles in photopolymer is a very effective method
to suppress temperature-dependent film-thickness and refractive-index changes as well as to increase the refractive
index modulation and reduce polymerization shrinkage.
Holographic manipulation of nanoparticle assembly in polymer and its applications to holographic 3D recording
and patterning are described. A statistical thermodynamic model is used to study the kinetics of multidimensional
nanoparticle assembling in polymer under holographic illumination. Volume holographic storage
using peristrophic multiplexing and nanoparticle pattering in silica nanoparticles-polymer composite films are
also demonstrated experimentally.
We review our recent works on nanocomposite holographic photopolymers doped with inorganic or organic nanoparticles that act as secondary mobile species and play an important role both in the refractive index modulation enhancement and in the suppression of polymerization shrinkage. Diffraction properties of volume holograms formed in several types of nanocomposite photopolymers are described. Experimental verification of the mutual diffusion of monomer molecules and nanoparticles during grating buildup is also described.
We describe the diffraction properties of organic nanoparticle-dispersed photopolymers in which hyperbranched
polymers (HBPs) act as transporting organic nanoparticles that increase the refractive-index contrast of a hologram.
We prepared HBPs by the living radical vinyl polymerization of inimers under ultraviolet-light illumination.
Such synthesized HBPs are easy to disperse into monomers without any aggregation, so that samples with
good optical quality are available. We investigate the role of HBPs in the recording process for two different
types of photopolymers capable of radical polymerization and cationic ring-opening polymerization. We also
evaluate the effect of HBP dispersion on recording sensitivities and polymerization shrinkage.
We describe a new type of nanocomposite photopolymer system in which nanoparticles having a large refractive-index difference from formed polymers are dispersed in monomers for permanent volume holographic recording. A model for the holographic grating formation based on the mutual diffusion of monomers and nanoparticles is discussed. The diffraction properties of volume holograms recorded in the nanocomposite photopolymer system are described. Experimental evidence of holographic control of nanoparticle-distribution morphology in a photopolymer is also shown.
We investigate the characteristics of ultraviolet (UV)-induced defect centers that leads to a transient broad absorption band extending from the near-UV to the near-infrared spectral regions in LiNbO3:Mg. The thermal activation energy of the UV induced defect centers was measured to be 0.65 eV and holes were found to be the UV-induced charge carriers. These results indicate that intermediate states O- act as the UV-induced defect centers in LiNbO3:Mg. In addition, we demonstrate nondestructive two-color holography by use of the UV-induced near-infrared photorefractivity in LiNbO3:Mg.
We investigate the dynamics ofholographic grating formation in methacrylate photopolymer films. Dual gratings consisting of
surface relief and volume holograms are observed. The influence of such grating formation on temporal behavior of the
diffiacted signal is discussed.
We investigate role of temperature-dependent ionic and re- created photocarrier (hole) gratings in self-enhanced readout from thermally fixed holographic gratings in undoped barium titanate. It is shown that the temperature dependence of the diffraction efficiency below approximately 80 degrees Celsius is mainly determined by temperature-dependent behavior of the dielectric and electro-optic constants. On the other hand, the trend of the ionic grating predominantly determines the temperature dependence of the diffraction efficiency above approximately 80 degrees Celsius even though a magnitude of the hole grating monotonically increases and is more than ten times larger than that of the ionic grating. This finding explains origin of the previously reported behavior of the temperature-dependent diffraction efficiency in barium titanate [D. Zhang et al., Appl. Opt. 34, 5241(1995)]. An activation energy of the mobile ions is also determined to be 1.05 eV from which shelf life is estimated to be over 150 days at 25 degrees Celsius.
Quantitative dependencies of a two-beam coupling time constant normalized by the photorefractive response time on a beam coupling gain and a pump-to-probe intensity ratio are measured experimentally. These resutls are also compared with numerical simulations.
A new method for implementing optically real-time wavelet-matched filtering is proposed by using nonlinear four-wave mixing in photorefractive media. In comparison with conventional matched filtering, the proposed method is able to give higher discrimination ability. Experimental results for optical character recognition are presented.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.